The present invention relates to niobium oxides, such as niobium suboxides, and further relates anodes and capacitors made therefrom.
As described in U.S. Pat. Nos. 6,759,026; 6,639,787; 6,592,740; 6,576,099; 6,527,937; 6,462,934; 6,416,730; 6,391,275; 6,373,685; and 6,322,912; and U.S. Published Patent Application Nos. 2005/0084445; 2004/0040415; 2003/0026756; 2002/0172861; 2002/0135973; 2002/0114722; 2001/0036056; 2005/0025699; and 2005/0008564 (all incorporated in their entirety by reference herein), niobium suboxides have been developed which are useful in forming anodes for capacitor applications. These powders, when formed into anodes, can have a capacitance up to about 200,000 CV/g or more and can have low DC leakage, for instance, from about 0.1 nA/CV to about 5.0 nA/CV. As described in these patents, the typical formation voltage for these niobium suboxide products, when formed into an anode, can be from about 6 to about 70 volts and preferably about 35 volts. These patents describe other high formation voltages, such as from 70 volts to about 130 volts. While these above-described patents describe a balance of properties with respect to DC leakage, capacitance, and formation voltage, as higher formation voltages are used, typically, the DC leakage increases, which can result from elevated electronic and/or ionic conduction in the dielectric layer at high voltage stresses. High conductivity can be a result of contaminants in the powder and a variety of defects generated during the anodization process, such as oxygen vacancies, crystallization, physical defects, and the like. Capacitor powder manufacturers have traditionally dealt with this problem by reducing the level of contaminants in the powder. However, this approach has technical and commercial limitations due to the high costs of purifying the materials, as well as other technical reasons. Accordingly, it would be highly desirable to stabilize the dielectric layer such that the charge carriers are immobilized or compensated thereby allowing the ability to form niobium suboxide powders at a higher formation voltage and yet preferably obtain low DC leakage.